linux-kernel - Re: [PATCH 5/5] uprobes: Change uprobe_copy_process() to dup xol

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Date:	Fri, 18 Oct 2013 17:49:34 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Anton Arapov <aarapov@...hat.com>, David Smith <dsmith@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Martin Cermak <mcermak@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] uprobes: Change uprobe_copy_process() to dup
	xol_area

On 10/13, Oleg Nesterov wrote:
>
> Unfortunately, uprobe_copy_process() can not simply do
> __create_xol_area(child, xol_area->vaddr). This could actually work
> but perf_event_mmap() doesn't expect the usage of foreign ->mm. So
> we offload this to task_work_run(), and pass the argument via not
> yet used utask->vaddr.

OK, this patch needs a fix, I'll send v2 in a minute.


> +	work = kmalloc(sizeof(*work), GFP_KERNEL);
> +	if (!work)
> +		return uprobe_warn(t, "dup xol area");
> +
> +	utask->vaddr = mm->uprobes_state.xol_area->vaddr;

Yes, currently utask->return_instances && !uprobes_state.xol_area
is not possible.

> +	init_task_work(work, dup_xol_work);
> +	task_work_add(t, work, true);

But if dup_xol_work() fails and the child does another fork(), it
can hit area == NULL, so we need to check this.

Oleg.

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